Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$87.84	12.758%	$99.0466	$99.05	$99.05	$99.00
Purchase #2	$19.30	8.116%	$20.8664	$20.87	$20.85	$20.90
Purchase #3	$87.80	6.873%	$93.8345	$93.83	$93.85	$93.80
Purchase #4	$136.75	10.521%	$151.1375	$151.14	$151.15	$151.10
Purchase #5	$72.87	7.560%	$78.379	$78.38	$78.40	$78.40
Purchase #6	$112.44	3.705%	$116.6059	$116.61	$116.60	$116.60
Purchase #7	$37.90	11.138%	$42.1213	$42.12	$42.10	$42.10
7 purchase totals =	$554.90		$601.9912	$602.00	$602.00	$601.90